Hitherto, silver salt photography was widely used as the most general method of obtaining multi-color images in the past because of its high sensitivity, high picture quality and ability to reproduce gradation. However, the silver salt photographic method has a disadvantage in that processing is complicated, involving processing in a development bath after imagewise exposure followed by conversion of the remaining silver halide to a silver complex salt which is soluble in water or to a silver salt which is stable in light.
The disclosure of dry type silver salt photographic light-sensitive materials in, for example, JP-A-59-48764 (the term "JP-A" as used herein means an "unexamined published Japanese Patent Application"), the disclosure of dye transfer type photographic light-sensitive materials, for example, in British Patent 249,530, and U.S. Pat. Nos. 2,020,775, 2,004,625, 2,217,544, 2,255,463 and 2,699,394, and the disclosure of silver dye-bleach type photographic light-sensitive materials, for example, in U.S. Patent 2,844,574, were made with a view to ameliorating these disadvantages.
Recording systems such as electrophotographic systems, thermal transfer systems, and ink jet systems which have a multi-color recording mechanism have been used in apparatus with recording materials in which silver salts are not used, but these systems have disadvantages in that the apparatus is large, in that recording fidelity is poor, and in that considerable effort is required to change consumables.
On the other hand, heat-sensitive recording systems do not suffer from the above mentioned disadvantages and if practical multi-color recording systems could be realized for this system they would be easy to use. There are methods in which heat-sensitive recording systems are used in which a plurality of color forming units are formed simply in sequence by increasing the thermal energy which is applied to provide color mixing and making change to render the hues impure, as disclosed, for example, in JP-B-51-19989 (corresponding to U.S. Pat. Nos. 3,895,173), JP-B-52-11231, JP-A-54-88135, JP-A-55-133991 and JP-A-55-133992 (the term "JP-B" as used herein means an "examined Japanese patent publication"). Other methods include those in which a decolorization mechanism in which a decolorizing agent operates at the same time when color forming units form colors at temperatures higher than the thermal response temperature and in which color units which have formed colors at low temperature are decolorized, as disclosed, for example, in JP-B-50-17868 (corresponding to U.S. Pat. No. 3,843,384), JP-B-51-5791, JP-B-57-14318 and JP-B-57-14319. However, there is a major problem with color hard copy of this type in that the number of colors which can be formed with these materials is small.
Recording materials in which heat-sensitive and light sensitive color forming systems, for example, are combined have been disclosed in U.S. Patent Application Ser. No. 07/174,306, JP-A-63-172681, JP-A-63-45084 (corresponding to U.S. Pat. Application Ser. No. 07/174,306) and JP-A-63-134282 (corresponding to U.S. Pat. Application Ser. No. 07/125,675) as multi-color recording materials which provide an improvement in respect of the above mentioned weaknesses. Thus, units in which a combination of diazo compound and coupler form a color forming component and/or units in which a combination of leuco dye and color developer form a color forming component are used as color forming unit layers in recording materials in which at least one color forming unit is established on either side of a transparent support and the color forming units form colors of different hues.
However, problems arise in respect of the fresh storage properties and the image densities of the recording material when a plurality of color forming unit layers is formed on the same side with recording materials of this type and so a transparent support is used and the color forming layers are formed on both sides of the support. This imposes a fundamental limitation in that non-transparent supports cannot be used for these materials, and it is inconvenient in respect of the fact that a new opaque layer has to be established during production.